One plane was hit by anti-aircraft fire but officials said it had returned to base safely while the "terrorist base" was "completely destroyed".

It was the first report of Boko Haram using anti-aircraft weapons.

Also on Friday, US Secretary of State John Kerry urged the Nigerian army to show restraint and not violate human rights as it pursues the militants.

Mr Kerry said there were "credible allegations" of "gross human rights violations" by the Nigerian military.

Last November, Amnesty International accused Nigeria's security forces of carrying out widespread abuses in their campaign against Boko Haram, including extra-judicial killings, enforced disappearances and torture.

The BBC has also received reports of civilians fleeing remote areas in Borno State and arriving in towns on the border with Cameroon.

More than 2,000 people have died in violence in Nigeria since 2010, most of which is blamed on Boko Haram.

The group, whose name means "Western education is forbidden", says its quest is to overthrow the Nigerian government and create an Islamic state.

There has been growing concern that Boko Haram is receiving backing from al-Qaeda-linked militants in other countries.

The current military campaign comes after Boko Haram last month rejected the prospect of an amnesty suggested by President Goodluck Jonathan.